This invention relates generally to display-hinged portable computers, such as notebook computers and hand-held computers, and more particularly, to hinge devices for attaching a display compartment to a microcomputer compartment.
A portable computer is a popular computer configuration enabling increased mobility for a user. Typically, a processor board, display and keyboard are integrated into a case having one or more compartments. A notebook computer typically includes a display compartment and a microcomputer compartment permanently attached in a hinged relationship. A flat panel display is mounted within the display compartment. A keyboard, microcomputer, data storage unit(s), expansion slot(s), and I/O ports are mounted in the microcomputer compartment. Modular peripheral units such as a floppy drive, hard drive, CD-ROM drive and modem or other PC card are readily installed and removed from the microcomputer compartment.
Electromagnetic interference is electromagnetic energy emitted from electronic devices which, either directly or indirectly, contributes to a degradation in performance of an electronic receiver or other electronic system. Poorly shielded electronic devices, for example, degrade radio and television signals resulting in audible or visible static at receivers picking up such signals, or cause other malfunctions of electronic equipment. Governments typically regulate EMI emissions to enhance public use of the radio wave spectrum and other electromagnetic wave spectrums. In the United States, for example, the Federal Communications Commission requires testing of devices and rates the devices by class according to their emissions. The Federal Communication Commission rates EMI emissions over a 120 kilohertz bandwidth. The 120 kHz bandwidth corresponds to the typical bandwidth of a conventional communication receiver, such as an FM receiver. Reduced EMI emissions within such bandwidth reduce the interference output perceived by a listener or viewer as, for example, static, white noise, or xe2x80x9cghosts.xe2x80x9d
Typical precautions taken by electronic manufacturers are to provide shielding of electronic devices to minimize EMI emissions. Computer manufacturers, for example, typically use shielded cables and shielded housings to minimize EMI emissions.
In a display-hinged portable computer there are conductive paths from the microcomputer compartment to the display compartment and a return path from the display compartment to the microcomputer compartment. The conductive paths are to carry power and data to or from the display device. The return path is to couple the display to a system ground, rather than have a display ground which is floating relative to the system ground. To leave the display xe2x80x9cfloatingxe2x80x9d could result in a larger voltage differential and more electromagnetic radiation. By coupling the display to a common electrical ground plane with the microcomputer and other computer modules, EMI emissions are reduced.
Conventionally, a ground wire or wire braid is used to form a return path for a display compartment. Such wires have had limited success in reducing EMI emissions. In particular, the wires form a non-zero impedance electrical connection between the display and system ground. The resulting voltage drop at high frequencies across such non-zero impedance causes undesirable EMI emissions. Such voltage drop acts as a voltage source which drives the display relative to the microcomputer, much like two elements in a dipole antenna. The result, for example, can be a vertically polarized EMI emission that fails to comply with regulatory emissions standards. Accordingly, complying with standards for EMI emissions in notebook computers is a continuing challenge.
According to the invention, a capacitor is formed at a hinge between a display compartment and a microcomputer compartment to reduce electromagnetic interference (EMI) emissions attributable to the display/microcomputer interface.